Misc. 37x14.5x15 swampers sxll won’t stay on bead

[jremo44]

I bought brand new super swamper sxll 37x14.5x15 and put them on brand new 15x10 wheels. Went off road trip this past weekend and within 20 minutes on the trail one popped a bead. Long story short 3 out of the 4 came off the bead. The 4th would have but i was in a good spot on the trail to change it out so i did. While i was waiting on spares to show up I found a stamp on the tire that said rim measurement 15x11.5. I can’t even find rims that size? Trying to make sense of all of this. I was running 20-22lbs pressure in all 4 and the terrain wasn’t anything crazy some mud holes and a little off camber stuff. I literally probably had 25 minutes total off road time and 3 out of the 4 went. Suggestions please